How to zero all values on a particular row?

[Barry Smith]

On Sun, 10 Jun 2007, Ben Tay wrote:

> Hi,
> 
> I need to insert values into a matrix and then solve this poisson eqn as
> part of my cfd code. For efficiency sake, I  simply use
> 
> "do j=1,size_y
> 
> do i=1,size_x
> 
>  matsetvalue ....
> 
> end do
> 
> end do"
> 
> to insert values into all the cells
> 
> Then for specific cells, I need to enter some other values. In other words,
> for specific rows of the matrix, I need to zero the whole row and insert new
> values. How can I do that?
> 
> I tried to use MatZeroRows but it says it's not for unassembled matrix. But
> I need to zero the particular row, insert values, and then finally assembly
> it. Is there a command to do this?

   matassemblybegin/end
   matzerorows
   matsetvalues, matsetvalues, matsetvalue
   matssemblybegin/end

   For improved efficiency you will want to call
   MatSetOption(mat,MAT_KEEP_ZEROED_ROWS); before the matzerorows()

> 
> Thanks
>